| Centrifugal pumps often convert operating conditions through different adjustment modes to meet the needs of flexible conversion of operating conditions.The current research on the internal flow of centrifugal pumps is mostly focused on stable working conditions.There are relatively few studies on the internal flow characteristics of the centrifugal pump throttle regulation and variable speed regulation in the transient process of variable operating conditions.At the same time,the research on the internal flow field and pressure pulsation characteristics of the centrifugal pump under stable operation lacks the combination with the actual working conditions.Therefore,the three-dimensional model of IS 80-65-160 centrifugal pump is established.The internal flow field and pressure fluctuation characteristics of the centrifugal pump under the stable condition of throttle regulation and variable speed regulation are analyzed.At the same time,by simulating the transient process of throttle regulation and variable speed regulation of centrifugal pump,the transient characteristics and internal flow mechanism of centrifugal pump in the process are revealed.The effects of valve regulating time and mode in throttle regulation and variable speed time and mode in variable speed regulation on transient process of centrifugal pump under variable working conditions are explored.The main contents and conclusions of this dissertation are as follows:(1)Analyzing the regulation principle of centrifugal pump under off-design condition and three-dimensional modeling of centrifugal pump are the theoretical and model basis for studying the transient process of centrifugal pump under off-design condition.Based on this,this paper analyzes the external characteristics and energy consumption characteristics of the centrifugal pump under different regulation modes combined with the operation regulation theory of the centrifugal pump under variable working conditions.The three-dimensional modeling and meshing of the IS 80-65-160 single stage water centrifugal pump are carried out.The results show that:Compared with throttle regulation,variable speed regulation has obvious advantages of energy saving.A three-dimensional model of the centrifugal pump was established and its reliability was verified.(2)The hydraulic performance of centrifugal pump is an important characterization of its internal flow characteristics.Few studies combine the operation regulation theory of centrifugal pump to analyze the flow mechanism in pump and guide the selection of centrifugal pump regulation mode in engineering.Based on this,this paper combines the performance and energy consumption of the centrifugal pump under throttle regulation and variable speed regulation,and uses CFX to numerically simulate the internal flow field under different stable conditions under throttle regulation and variable speed regulation,to explore the internal flow field response and pressure pulsation response characteristics of the hydraulic performance and vibration characteristics of the centrifugal pump under different regulation modes.The results show that:(1)The energy saving and stability advantages of variable speed regulation are gradually obvious with the increase of flow regulation range.For this pump,the flow field response in the pump corresponding to the efficient operation of variable speed regulation is mainly to improve the flow pattern in the impeller,the tongue and the inlet section.(2)The flow operating condition is an important factor to determine the pressure pulsation intensity,In variable speed operation,the internal response of high stability performance of centrifugal pump is mainly to reduce the vibration amplitude of impeller and tongue.(3)Throttle regulation is a transient process with variable flow rate.The hydraulic performance and internal flow characteristics in this process need to be analyzed in depth.At the same time,there is also a lack of effective guidance for determining the regulate valve time and regulate valve mode of throttling regulation.Based on this,CFX is used to simulate the transient process of throttling regulation with variable flow rate,and the hydraulic performance and internal flow performance of centrifugal pump in this process are analyzed.The influence of valve regulation mode and valve regulation time on the transient process of throttling regulation is explored.The results show that:(1)In the transient process of throttling regulation,the streamline distribution in the pump is more concentrated,compact and has obvious transient effect.Different parts of the pump are subjected to different degrees of pressure and velocity shocks in the transient process.(2)Centrifugal pump has stronger transient effect in the transient process of throttling regulating flow with shorter regulating valve time.Under the exponential valve regulation mode,the transient effect of centrifugal pump throttle regulating flow transient process is stronger at the initial time,and the external characteristic parameters and internal pressure and velocity change more intense.(4)In the transient process of variable speed regulation,the hydraulic performance span of centrifugal pump is large,and the research on the internal flow characteristics in this process is relatively small.At the same time,in the application level of variable speed regulation technology in engineering,the selection of speed change mode and change time lacks the consideration of internal flow characteristics of centrifugal pump.Based on this,this paper builds a centrifugal pump pipe network system with Flowmaster software,obtains the boundary conditions of the transient process of centrifugal pump variable speed regulation and takes CFX software to simulate the transient process of centrifugal pump variable speed regulation,and reveals the transient characteristics and internal flow mechanism in the process.At the same time,the influence of speed change time and mode on the transient process of variable speed regulation is explored by introducing the control system evaluation index and combining with the flow field analysis in the pump.The results show that:(1)The dimensionless external characteristic parameters in the transient process are significantly different from those in the quasi-steady state process.In the transient process,the flow field in the pump has higher turbulent kinetic energy level,stronger vorticity and more concentrated streamline distribution than the quasi-steady state assumption.(2)Variable speed regulation process has obvious stage characteristics.In stage II(0.1s<t<0.2s/0.4s),the external characteristic parameters of centrifugal pump and the flow field inside the pump change most dramatically.(3)The shorter the speed change time is,the stronger the transient effect of centrifugal pump is,and the stronger the synchronization of the external characteristic parameters with the speed is.In general,the hydraulic performance of the centrifugal pump in the transient process is more excellent under long time and exponential speed. |
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